1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device which handles signals at high speed, and to a semiconductor device which has capacitors for reducing power source noise.
2. Description of the Background Art
FIG. 22 is a perspective view for describing a typical structure of a conventional semiconductor device of the above type. FIG. 23 is a cross-sectional view for describing the semiconductor device shown in FIG. 22. In these FIGS. 22 and 23, reference numeral 1 indicates a system substrate on which to mount components. Reference numeral 2 indicates a BGA (ball grid array) substrate mounted on the system substrate 1. As is well known, numerous solder balls 3 are interposed between the BGA substrate 2 and a principal plane of the system substrate 1 to keep the two substrates fixed and electrically connected. Reference numeral 4 indicates a semiconductor chip mounted on the BGA substrate 2. As shown in FIG. 23, bumps 5 are interposed between the semiconductor chip 4 and a principal plane of the BGA substrate 2 to have the chip and substrate fixed and electrically connected.
Reference numeral 6 indicates chip capacitors mounted on the system substrate 1 and BGA substrate 2. A large number of chip capacitors 6 are interposed connectively between power supply terminals (not shown) on a semiconductor device that handles signals at high speed; these chip capacitors 6 are provided to reduce power source noise and thereby to stabilize voltage levels of the power source and ground.
Given the above constitution, one disadvantage of the conventional semiconductor device is that the chip capacitors 6 are located away from the semiconductor chip 4. Therefore, as the speed of signals, which are handled by the semiconductor device, is higher, the inductance between the semiconductor chip 4 and the chip capacitors 6 becomes higher. The growing inductance progressively reduces the immunity of the chip to power source noise.
Another disadvantage is that the flow of high-speed signals generates electromagnetic waves from the semiconductor chip 4, its package, or its mounting substrate. When reaching nearby electronic equipment, the electromagnetic waves can induce electric currents therein by electromagnetic induction, triggering a malfunction at times.
Further, semiconductor chips are mounted on the system substrate basically in a two-dimensional manner. This leads to another problem: semiconductor chips, as they are designed to become ever higher in performance, incorporate a growing number of I/O terminals which translate into an ever-greater external size. On that extended component scale, differences in thermal expansion coefficient between the semiconductor chip 4 and the system substrate 1 can result in a warped substrate or dislodged terminals. Here, “dislodged terminals” means that the accuracy of location of terminals is changed for worse.
Therefore, above-mentioned flaws make it difficult to mount semiconductor chips 4 precisely on the system substrate 1. The yield rate of the chip 4 thus tends to decline and the reliability of mounting worsens.
The BGA type semiconductor device is at its limit of fabrication when coming to measure about 40 mm per side. When large-sized devices carry numerous terminals, they may adopt a pin grid array structure. The pin grid array structure, however, requires installing a socket between the semiconductor chip and the mounting substrate, which raises fabrication costs.
Multi-chip modules (MCM) have different external shapes and different numbers of terminals from one system to another. Such diversities make it difficult for the modules to share sockets and substrates between them. This is another factor pushing up the costs involved.
Another problem with the BGA type is that the module or chip is not receptive to what is known as rework. That is, considerable difficulties are experienced when a semiconductor device or MCM is dismounted from the system substrate for repair or for replacement with a new one having higher performance and the repaired or a replacement device is again mounted onto the system substrate.
Furthermore, the heat dissipating structure of the BGA type leaves much to be desired in terms of performance and production costs.